The present invention generally relates to noise attenuation in vehicle drivelines and more particularly to an improved noise-attenuating propshaft and a method for its construction.
Propshafts are commonly employed for transmitting power from a rotational power source, such as the output shaft of a vehicle transmission, to a rotatably driven mechanism, such as a differential assembly. As is well known in the art, propshafts tend to transmit sound while transferring rotary power. When the propshaft is excited a harmonic frequency, vibration and noise may be amplified, creating noise that is undesirable to passengers riding in the vehicle. Thus, it is desirable and advantageous to attenuate vibrations within the propshaft in order to reduce noise within the vehicle passenger compartment.
Various devices have been employed to attenuate the propagation of noise from propshafts including inserts that are made from cardboard, foam or resilient materials, such as rubber. The inserts that are typically used for a given propshaft are generally identical in their configuration (i.e., construction, size, mass and density) and are installed in the propshaft such that they are equidistantly spaced along the length of the propshaft. Construction in this manner is advantageous in that it greatly simplifies the manufacturer of the propshaft. Despite this advantage, several drawbacks remain.
For example, symmetric positioning of the identically-configured inserts within the propshaft typically does not maximize the attenuation of the vibration within the propshaft. Accordingly, it is desirable to provide an improved propshaft that attenuates vibrations within the propshaft to a larger degree than that which is taught by the prior art.
In one preferred form, the present invention provides a shaft structure and at least two insert members. The shaft structure has a longitudinally-extending cavity and is configured to vibrate in response to the receipt of an input of a predetermined frequency such that at least two second bending mode anti-nodes are generated in spaced relation to one another along the longitudinal axis of the shaft structure. The insert members are disposed within the longitudinally extending cavity and engage an inner wall of the shaft structure. Each of the insert members is located at a position that approximately corresponds to an associated one of the anti-nodes and has a density that is tailored to an anticipated displacement of the associated anti-node. A method for attenuating noise transmission from a vehicle driveline is also disclosed.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.